A processing performance of a semiconductor chip (IC chip) used for an electronic device such as a high-performance server and a high-speed network device has been improved year by year. Also, along with the improvement of the processing performance of the IC chip, a signal transmission speed between the IC chips and between the IC chip and a communication module has risen steadily. For example, while a mainstream signal transmission speed is about 10 [Gbit/s] so far, it is expected that the signal transmission speed will rise up to about 25 [Gbit/s] in near future.
Under the above-described circumstances, low power consumption of the signal transmission device, downsizing thereof, improvement of a cooling performance thereof, and others are desired. For example, if the signal transmission speed is risen to about 25 [Gbit/s], a compensation circuit for signal waveform shaping is essential even if a signal transmission distance is about 10 cm, and therefore, the power consumption of the signal transmission device is increased, and besides, it is also required to secure a space used for mounting the compensation circuit. Further, a calorific value of the communication module is also increased, and therefore, a size of a cooling mechanism for the communication module is necessarily increased.
As described above, while various demands for the signal transmission device have occurred along with the improvement of the processing performance of the IC chip, the cooling mechanism for the communication module is focused here. A heat sink is cited as one example of the cooling mechanism for the communication module, and conventional signal transmission devices can be roughly categorized as follows based on a mode of the heat sink. That is, the conventional signal transmission devices can be roughly categorized into a type in which the heat sink is individually provided for each of a plurality of communication modules (see Japanese Patent Application Laid-Open Publication No. 2010-175995 (Patent Document 1))) and a type in which a common heat sink is provided for the plurality of communication modules. Accordingly, in the following explanation, the former and the latter are distinguished from each other as an “individual type” and a “collective type” in some cases, respectively.
Indeed, in both types of the signal transmission device, the heat sink is arranged on the communication module. More specifically, in the individual-type signal transmission device, a heat-transfer plate of the heat sink is placed on a top surface of each of the communication modules, and a plurality of heat-release fins stand on each heat-transfer plate. On the other hand, in the collective-type signal transmission device, the heat-transfer plate of the heat sink is placed on top surfaces of the plurality of communication modules so as to collectively cover these modules, and the plurality of heat-release fins stand on a common heat-transfer plate. That is, the individual type and the collective type are common in that the heat-release fins of the heat sink are arranged in an upper portion of the communication module.